In a turbine applied for a power generating system, a seal part is provided at a gap between a static part and a rotation part so as to reduce leakage of working fluid from the gap between the static part and the rotation part, and to improve performance. Conventionally, a metal seal made up of a metal material is used as the seal part. Besides, a ceramics seal made up of a ceramics material is used as a seal part for high-temperature. As the ceramics seal, the one having an abradability function which is intentionally abraded between the static part and the rotation part is known from a point of view of making a clearance between the static part and the rotation part small and suppressing damages of the static part or the rotation part. The one which is porous and has a large porosity is known as the ceramics seal having the abradability function.
Besides, a labyrinth seal part formed in a concave and convex state is provided by processing one side or both sides of facing components between an end part of a rotor blade and a shroud segment facing thereto or between a stator blade diaphragm (inner ring) and a turbine rotor facing thereto so as to reduce the leakage of the working fluid between the above-stated facing components and to improve an operation efficiency.
In recent years, needs to make a turbine high-temperature and high-pressure is increasing from a point of view of efficiency of power generation. As a turbine made to be high-temperature and high-pressure, a usage of a CO2 turbine is studied. In the CO2 turbine, combustion gas in which fuel such as natural gas, oxygen, and CO2 are mixed and burned is supplied, and the rotation part is rotated while using supercritical CO2 as a medium to generate electric power. In the CO2 turbine, it is possible to collect CO2 generated by combustion as it is, and therefore, it has been focused from a point of view of global environmental protection because it is possible to effectively use CO2, besides NOx is not discharged.
However, components are easy to become high-temperature in the CO2 turbine compared to a conventional turbine because the combustion gas becomes high-temperature and high-pressure, and a heat transfer of the combustion gas is large. Accordingly, there is a possibility in which a desired sealing effect cannot be obtained by a conventional metal seal. Namely, there is a possibility in which the combustion gas leaks and it becomes impossible to maintain a differential pressure between an upstream side and a downstream side of the rotation part.
Besides, the ceramics seal, specifically the ceramics seal having the abradability function is also known. It is conventionally applied for a component in which strength is not required, and the facing component forms a blade having a sharp tip by processing a metal material. Accordingly, a coating film having a smooth surface, porous and with the large porosity is used for the conventional ceramics seal. On the other hand, in the CO2 turbine in which the combustion gas becomes high-temperature and high-pressure and the heat transfer of the combustion gas is large compared to the conventional turbine, it is necessary to use ceramics also for facing concave and convex parts, and the conventional ceramics seal which is poor in strength is not necessarily suitable.
Besides, a temperature of fins of the labyrinth seal part becomes high also when the labyrinth seal part is provided, and it becomes a cause of thickness-reduction damage. When a degree of the thickness-reduction damage becomes large, performance of the turbine is lowered because the leakage of the working fluid increases.